CPUFirstly, the CPU. If it's gaming you want, you're going to need an absolute minimum of 2.2GHz, but if you go that low, don't expect to be able to play the latest games. Realistically, you need at least 2.4GHz, but if you have the money, you can go right up to 3GHz- but that's just overkill.
I'm sticking with Intel here, partly because I think they're better than AMD, and also because I know the Intel chips pretty well. So, unless you have a lot of cash to spare, you not going to be getting a Core 2 Extreme- so we'll stick with Duo and Quad. The Duos run from 1.33GHz up to 3.06GHz and the Quads from 2.33GHz to 3GHz. I'd recommend a Quad fro several reasons:
*The lower end ones are cheaper than the higher end Duos
*They have higher bus speeds
*and larger caches
So from now on, I'll assume you get a Core 2 Quad. You'll want a 45nm one, as opposed to 65nm, so depending on how much money you have, you'll be looking at 2.5-3GHz for your laptop.
RAMSimple. 2GB ABSOLUTE minimum, but you're best going for 4GB. RAM is cheap and to play the new games you'll need as much as you can get.
GPUYou need a dedicated GPU- no more integrated ones. For me, and most other people, nVidia is the best here. For a laptop, I recommend either the GeForce 8600 GT. This'll cost you about £40-50. If however you have a bit more to spend, have a look at the GTS 250, but this'll cost just over twice as much.
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Those are the three biggies there. Obviously you'll have to sort out the screen size and other stuff for yourself- that's just personal choice.